The expected device behavior after updating a Line of Business (LoB) app package that is already deployed on a device depends on the specific app and how the update is configured in Intune.
Generally, after the update is pushed to the device, the user will be prompted to install the update. If the update is mandatory, the user will not be able to use the app until the update is installed. If the update is optional, the user will have the choice to install the update at a later time.
Once the update is installed, the user should be able to launch the app and use the updated version. However, there may be some cases where the app needs to be closed and restarted to fully apply the updates.